I'm embarrassed to say I have first-hand experience what contamination can do in brake fluid. 20 years ago I did a complete brake job on my 74 Torino. Instead of brake fluid I flushed the system with mineral spirits. I drove the car 20 miles before the car started going slower and slower and the brakes pretty much locked up. The rotors overheated with a blue temper color on the surface. I had the car towed home where I replaced the master cylinder and the brake seals on all four corners of the car.

Petroleum-based fluids are incompatible with the compound used to make brake seals. The seals will swell if it sees the wrong fluid.

The reason this happened is because I decided to put mineral spirits in an empty brake fluid container. I liked the container. Because of this incident, to this day I make sure everything is properly labeled on my shelf - garage and home.

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95 E320 Cabriolet, 169K